Not a major problem at the moment since the noise has now disappeared but yesterday I developed a noise that matched engine speed and load exactly. There was a component that sounded like the "pop-pop-pop" that you would expect of a small exhaust leak. However, there was also a component that sounded like flapping - my wife thought it sounded sorta like a baseball card flapping against bicycle spokes. One could also imagine that it sounded like a belt with a loose edge hitting something.

On acceleration, the noises would generally increase but would not necessarily go away on deceleration, although it would diminish greatly. At no point was it loud, leading me to suspect that it was a smallish leak someplace. My suspicions are that it could be 1) a head or exhaust manifold gasket leak (unlikely since it has now gone away), 2) a leak around some component that inserts into the exhaust piping someplace (air injection? O2 sensor?), or 3) a joint in the exhaust. Does the exhaust use one of those doughnuts to allow engine movement without flexing the exhaust system? If so, that may be the culprit and could explain the noise going away since the doughnut may now be settled into a position where the leak is blocked.

I'm open to any suggestions to help decipher this. No CEL, no engine roughness, oil level is fine, etc.

 

The timing chain tensioner has been known to make the "card in a bicycle spoke" noise, usually at co ld start.

 

I was wondering about things like that even though this was after being fully warmed. Would it change nature on + vs. - acceleration?

 

As far as a leaking header donut....unless someone did a real shady job doing a mod or something, I doubt this is the problem. It's almost a foolproof design.

Tensioner....I've found the tensioner makes most of it's noise at idle and low revs. But....I have seen them make constant noise through the whole rev band.

A sound clip would be the only way to do this right. Like using a vid camera, and circling the engine while filming it. Bigpurp did this I instanlty knew he needed a chain tensioner.

 

I'll be on the lookout for a recurrance and will let you know.

Thanks for checking in.