Idle ticking disappears with revs

Hi All, first post here and most happy to be in the community! Can use some help, I have had my 1999 911 996 C2 Cab for ten years, 6 speed manual, 50,000 miles, California car since I had it, don't know any history before that though. I was told the IMS bearing had been done. Recently, I have changed the oil and filter, mobil 1 0w-40, (old filter free of debris) air and cabin filters, fuel filter, plugs (not coils) water pump, low temp thermostat, vacuum coolant flush, transmission fluid removal/replace, upper idler pulley and serpentine belt. Now the problem, I have engine idle ticking, bank 2 side is where its most prominent, mostly comes, but does go away for a minute or so, then return, I can hear it only at idle, if I turn on the AC to increase the revs or depressed the throttle ever so slightly it goes away. Clutch in, clutch out doesn't make a difference. With a mechanics stethoscope, I can hear it more at the bottom, at the exhaust manifold, almost non existent with the slightly higher revs when the ac is on, this has been going on for a few thousand miles or more, all my searches point me to piston slap, bore scoring, sticky lifters....etc. I do not have any abnormal smoke or soot inside either tailpipe, no oil level fluctuations over the last 1500 miles. Dropping the sump and scoping from the bottom are in my future, however right now I'm looking to you all for some additional possible causes. I'm attaching a couple of clips, one at idle and one at idle with slightly increased revs. A different set of ears would greatly be appreciated. Any and all thoughts are welcomed. Thanks in advance! Idle ac on

Guaranteed you�ll get many responses. I recommend you spend few hours and watch Jake Raby�s entire bore scoring video series on rennvision if you haven�t already. Good luck.

I recommend you take your stethoscope and listen to the cats. I have heard more than a few make this ticking sound, and was mistaken for a piston slap or lifter noise.

Sorry this comment is probably of no help but I had exactly the same thing with my 996C2, it drove me nuts. Drove it for 3 years (tracked it twice) and 55,000 km's and it never got any worse.

Noise on top does not sound like bore scoring to me. Bore scoring is more noticeable from underneath/along side the rear of car. The underneath passenger shot sounds kinda like an exhaust leak to me or perhaps a loose spark plug as they were recently changed. On third listen maybe I'm just hearing the exhaust. Not sure about top side tapping. BTW I would change the water tank. When they get that yellow they have some age and susceptible to cracking on the back side and leaking.

The topside quick tick sounds like the "regen valve" that's located on the top left side of engine. Toward the end of the first video there's another louder tick that comes in - still doesn't sound like piston slap to me - could be the belt tensioner or idler pulley, or and of the other rotating things located at the back of the engine (alternator, AC pump, idlers, power steering pump etc.). An invasive borescope from the sump will rule that out - until then everything is a guess. Good luck

Quotes source posts: 16033056, 16033228, 16033264, 16033456, 16033679

Thank you for the responses so far I've run through those and there very good, don't quote me, but in all the videos of bore scope I've seen all the engines are at idle....I haven't seen any where there is some throttle added, what happens to the ticking noise when its under load? I my case, with the increase of another 100 or so rpms, I don't hear it. I did hover around the cats, although I could hear it there slightly, its more towards the front where the manifold meets the cylinders. I'll give another listen I only hear when I'm stopped, I'm thinking I'll just leave the AC on all the time... problem solved I hear you, on the list, trying to wrap my head around this one The louder tick is the one I'm trying to track down, I put a ear to all the other rotating bits, nothing of note gave me the ah ha moment I've been looking for. Seems like the responses so far are moving away for my fear of cylinder score. I'm hoping a couple of other trained ears will chime in, the more the merrier. Much appreciated.,

Quotes source post: 16035124

Don't "hover" around the cats, place the metal probe/sensor firmly against the cat, compare bank 1 to bank 2.

Leaking manifold gasket?

A friend of mine has the same exact car as you 99 c2 cab. We pin pointed the sound coming from bank 2 in between cylinders 4 & 5. Bore scoped top and bottom and had no scoring, no oil consumption, sound doesn't get louder with revs, driver tail pipe is not sooty, no white smoke on startup. Thinking it's a lifter (rare), cam pad, timing guides, or tensioners. Nobody has an exact answer from what I've searched. Car drives perfect no CEL. Checking cam deviations is probably the next step, but neither of us has a durametric at the moment.

Will do, unfortunately won't be until the weekend. Although the sound is further back, would a failing cat register noise back towards the block? I appreciate the advice.

Now there's three of us on this thread with like symptoms, good to hear the bore score scope was negative. Your right, I to have yet to find any answers in my searches, hopefully there are others out there who have run across this and can report in with there thoughts/findings.

Timing chain tensioner(s) Worn guide Worn crank pilot bushing bad bearing in Alt/Waterpump/tensioner/AC clutch Ac clutch tired, they can be rebuilt if you can find the bearing and a friction disk. cracked/broken baffle in muffler.

Take the belt off and listen if the noise has gone. If it has, then the cause lies with one of the bearings in the belt driven systems

I still say check your header gasket. Mine did the same.

I have the same noise on start-up until the engine warms. New Fab Speed Cats and Mufflers, Coil-Packs replaced within 10k (ticking before their replacement). I'm thinking timing chain tensioners, but I don't drive it more than 50 miles a month...

Quotes source post: 16036041

Please update this thread if you happen to get the deviation readings. I�d be curious to see if there�s any sort of possible correlation.