M35 Idle Exhaust Bump / Burp Weird

[Arlo]

So just yesterday I was sitting at a light and i felt this little bump after I came to a stop. I first thought it was my transmission downshifting late but after I came to a stop again it repeated over and over.

It's a weird sound/feeling. The car can be in park and idling at a rock solid 650rpm. Every few seconds it will just bump. I can feel it too. I listened to the engine and it sounds just as good as the day i bought it but when i listen to the exhaust i hear it.
I have no CEL and no noticeable performance issues.

Please watch the video. It occurs @ seconds 11, 13, 16 & 33.

http://youtu.be/Q6GNOgC7cEs?list=UUNS_z ... B9k0zO5ATA

Any ideas?

[svard75]

I think it might be better for you to idle the car and walk around, open the hood listen and look at any moving parts while its knocking. Its much easier to find this since it happens when youre idling. Does it increase in loudness or speed when driving? Could be the ac clutch trying to engage, or the belt idler, or exhaust heat shield or bad catalytic or broken exhaust hanger. Stop at a parking lot with someone watching out for you and lay down at every side listening and looking with a flashlight. If you have access to a lift and only after the car is cool grab each component of the exhaust and shake it as hard as possible.

[Arlo]

Funny thing is that I did just that. I actualy took video of the engine while sitting at idle. I can hear nothing. I just purrs along like nothing is the matter.

The feeling disappears while driving. It hums along like it always has. I can honestly dismiss the A/C as it's not on. It's fall in Northern Virginia. ALhtough you may have something with the bad cat. But if that were the case wouldnt i get a CEL?

[svard75]

Not immediately. I have a bad cat and each time i clear the SES light it takes a few months to come back. As i said lift the car and shake the exhaust.