I’ve had this happen for a while now and have just been ignoring it because I assume it’s probably minor but I was wondering if anyone has experience this.

it generally only happens when towing up a grade. Usually when the rpms are around 4k. At first I thought it may be spark knock but it doesn’t quite sound like that. I’m thinking it almost sounds like a heat shield or a catalytic converter rattling.

there isn’t anything that I can tell is loose. I don’t hear anything when whacking the cats with a hammer. It starts to happen about 10 seconds into being under a heavy load up a hill I guess when things start to heat up. Oil pressure is good. Engine temps are good. And there’s no loss of power at all. No codes, live data on hptuners looks good.


Also for anyone wondering how well an 08 with a magnacharger tows. The answer is really well. We towed a 9000lb boat and trailer up and down the hills around lake Lanier with heavy traffic in some places. It had plenty of power and felt surprisingly confidence inspiring. I didn’t use a weight distributing hitch and the truck didn’t even really squat. It was about 75-80 degrees out and trans temps never climbed above 180 with the trucool 40k installed. There’s no way the truck would’ve done it with the stock cooler.

Overall im pretty impressed. It did way better than my mom’s f150 the last time we had to tow a boat. I guess there’s really no replacement for displacement!

 

Bent ladder type skid plate. Makes contact with hot exhaust pipe. Check for clearance on driver side. Exhaust pipe expands under heat, and engine vibrates more under load and torques the pipe to make contact with skid plate or driver side heatshield in same area.Voila!

I also installed thin round rubber isolators on its 4 mounting bolts to eliminate known rattle problems.

If the ladder plate is bent, I have an easy solution to straighten it out. If u crawl underneath and check for clearance, you will see all is OK. Because it happens only when moving. So hard to pinpoint. Easiest way to do this is to pull off one or both plates to see if it goes away. If not, pull front skidplate or t-case plate and check again.

Tell us if it worked!

This took me 6 months to figure out. GM dealers had no clue.

 

hey thanks I’ll look into that. I had my exhaust done and they did 2x 2.5 inch pipes that go over the axle. It is just barely hits and rattles really loud at a stop only when it’s really hot. I’ll have to check and see if my skid plate is bent and it’s rattling there too. I did also have that rattle before my exhaust was done.

it so weird. It almost sounds like spark knock and only happens after going up a grade for a little while at high rpm and it takes a second to go away even after reaching the top and upshifting which makes me think it’s just something rattling. Especially since there’s no noticeable loss of power.