I've had my RST for about a month now. I've been running it a lot with the windows up and the AC on so I've started to notice the rattles and other sounds.

4.8, 5 speed, JBA shorties, K&N and the dual exhaust that comes with it. It makes a rattle that almost sounds like an exhaust leak but I've been all over it and I cannot find anything around the headers. I even tightened up the bolts that connect the Y to the catback.

The time it is noticeable is while the engine is under load. If it is parked or coasting in neutral I can rev the engine and it doesn't rattle. That seems to me that it is not a leak. Makes the sound regardless if the AC is on or not.

No metal in oil change, good oil pressure and not running high temperature.

I wish I could get a sound bite in here but I can't pick up the noise with my camera. Go figure. This is my first V8 with a manual. The 4.3 I had also had some rattles that I never figured out. Using 93 octane. Would using 93 instead the 87 that it had been running on for the last 6 years cause it?

Want to know if it's screwing up because I'm getting tuned on Thursday. If it's not 100% I don't want to waste my time or Justin's @ Blackbear.

 

Does it increase in pitch or loudness with rpm or speed?

 

The only bad rattle i had with my RST was the tail pipes rattling against the roll pan where they come through it.

 

I had a horrendous rattle that would only be noticeable when crusing down the highway. Turned out being a exhaust heat shield.

 

It gets louder with the rpm. Lets say I'm cruising at 60 and decide that I want to go 65 so I increase the RPM to get up to 65. After it hits 65 and I cruise at that speed. The sound goes away.

 

So it gets louder under load.... crawl under your truck and shake the exhaust with your hand and see if you can get it to hit anything.

 

Are you sure that it's not detonation? I'd also check the exhaust heat shields and try hitting the cats and muffler with a rubber mallet...

 

Does the sound go away when you push in the clutch pedal? Almost all the manual clutch trucks make noise in the throwout bearing. Listen carefully when you push the clutch in, I bet it goes away.

 

I've thought about the noise there. I'll go for a drive in the morning see what I can hear.

 

My 97 NV3500 does it - my '04 NV3500 does it, my 03 GMC sonoma did it (sold) and my dad's '03 sonoma did it as well (both nv1500 trannies)