What could be causing rattle/knock?

[zigm]

I hear a soft knock/rattle that sounds like it is coming from the rear of the engine on the passenger side. I'd say it sounds like a lifter if I had to describe it.

Idle in Park = no knock/rattle
Idle in Drive = no knock/rattle
~1800rpm in Park = no knock/rattle
~1800rpm in Drive while on the road = KNOCK/RATTLE

The sound seems to fade away after about ~2400rpm, but it may just be masked by the engine getting louder in general.

The car idles fine and runs strong... no obvious signs of an engine or tranny problem.
Oil pressure is a solid 50 to 60psi @ 70mph & 20psi at idle with 20w50 Valvoline race oil (the street version).
I cut open my oil filter at last change, and did not see any debris.
All push rods are turning, nothing loose under passenger valve cover.
Both headers have been removed - no cracks found

Things still on the 'to do' list:
Pull driver valve cover and inspect
check flywheel & TCC for loose bolts or other issues

Can anyone offer advice/experience on this type of knock/rattle? please please please don't let this be a rod knock that requires a rebuild.

thanks,

 

[turbojd]

Is the downpipe contacting anything under a load?

 

[forcefed3.8's]

Loose TC bolts is my guess.

 

[dproberts05]

noise

I get the same noise, it's from my downpipe bumping the frame.

 

[turbolou]

with the car in park grab the throttle & wing it a bit.( don't over do it ) If you can duplicate & make the knock come & go or change you probably have a rod bearing failure.Loose converter bolts or cracked flywheel will be more noticeable going from neutral to drive at idle & sound changes as that's done. Check crank pulley bolts,Adapter plate that the a/c compressor,alternator,P/S pump bolts to. the attachment bolts to the head are hard to see can come loose & cause a rattle. good luck

 

[87NAT]

Loose TC bolts is my guess.

+1

 

[zigm]

Update: Noise is still present after verifying TCC bolts were tight.

Pulled TCC cover off tonight and checked bolts: 3 were tight, one was 1/4 turn loose. I coudn't get to the flywheel bolts, but they all visually looked good. I did not see any issues with the flywheel.

I can see plenty of daylight surrounding the downpipe & I have a torque strap... I can't see any indication it is hitting the frame.

If I put the transmission in N while going down the road and bring the RPMs up to ~1800 the noise is not present. It seems that either the problem is transmission related, or requires some level of 'load' to be on the engine.

I cannot create the sound while ithe transmission is in Park... building boost on the footbrake up to ~1800rpms WILL create the sound.

I continue to work on the items Lou mentioned. If I get brave enough this weekend, I'll let my wife do the brake-stand while I crawl around/under the car trying to narrow it down.

thanks,

 

[turbolou]

Take a pry bar & check the end play on the crank to make sure you haven't smoked the thrust main. shouldn't be hardly any end play. Sounds like the crank could be hydraulicking forward when applying a load such as you described foot braking it.