Kind of hard to explain but ill try.

This started about 2 weeks ago, when I go anywhere from 50 miles on hour on up, then let overdrive kick in and cruise then ever so slightly put my foot on the peddle to stay at that speed, or even give it a little gas 80% of the time it makes this weird sound kind of like my vents are turned on but louder. It sounds like its coming from the engine area and on the passenger side door part of the truck, then at the bottom around my feet when it makes the noise it feels like there is a slight grinding to something spinning somewheres under my floor board... maybe, that part could be in my head because im a worry nut. If I punch my gas, or even just slowly ease into the gas peddle it gets louder, then when I hit about 2700 RPM or higher the noise goes away.

At first I thought it was an exhaust leak, I belly up and start looking for leaks. Right off the bat I found 3 cracks in my muffler, I think awesome! Just replace the Flowmaster 40 and im good to go, nothing expensive.. NOT! I just got back today from getting it replaced and its still making that sound, that blows.

When I got out my truck I smelt like a rubber burning, I start looking around and there was smoke fading away from the rear/mid left driver side of my truck, I couldnt find where it was coming from and the smell eventually went away. It wasnt much smoke, just a little fyi.

I called the shop who replaced the muffler and he said the only thing he used was WD40 when welding... im a half *** welder myself and I cant think of what i'd use WD40 for, but I wouldnt think that'd be the problem.

So yeah, weird noise, think its the muffler so I replace it, weird noise still there + new burning rubber smell / a little smoke. Keep in mind this only happens when its 50 miles an hour or higher when over drive kicks in and it just cruises on the freeway or on a road unless I give it more gas it gets louder then kicks off. Anything from 1 - 45ish where your running at a higher RPM it doesnt make the noise.

EDIT: Its a 98 1500 Crew Cab Short Bed, 5.9

 

I'm not sure.. but there may be a vacum leak somewhere that could be making the noise.. could be your vents are not shutting all the way and when vacum builds they start to move and make weird noises coming from the dash... but it's hard to say with out actually hearin git and looking over the truck

 

Hmm, well maybe if you have a camera that can take audio as well you might want to try that and throw it up on here so we can hear it. (be safe doing it while driving). But without hearing it i would have to agree with iwhitne that it might have something to do with a part of your vacuum system. Mine has a slight whistle when im going over 50 (leak somewhere on the windshield thats letting in air at higher speeds)

 

The higher the RPMs(or even HPMs lol) the more sound the truck will make.

 

I know what you're getting at Purp, not to be rude but ive had the truck for a good while now, I know its naturally going to be louder at a higher RPG, specially with a FM40 on it, but im talking about the added noise its been making lately when driving at a higher MPH. Its different then its been since I bought the truck, and not a good sound hehe.

I dont think I can get a sound audio of it, all I have is my cell phone which isnt saying much. Looks like i'll have to bite the bullet and take it in to get it fixed if I cant find it on my own, which doesnt look like its happening.

 

At what RPMs does it make the sound?

 

Is it a 4x4?

 

Yes its 4x4, ive maybe put it in 4 wheel drive a total of 8 times since ive owned it in the last year and a half, and the last time I did was 6 - 8 months ago.

When it settles out at 50 miles an hour it cruises about 1100-1200 RPM I believe. When I barely give it gas and it makes that funky noise its around 1300-1400, then I can ease into the gas on up to 2400ish and it goes away as I continue to give it more gas and allow the RPM to climb.

If im on the freeway and let it settle/cruise out at 70 miles an hour its around 1700 RPM, then the same thing when I give it a little gas funky noise comes back until I give it enough where it kicks up in gear and RPM goes up, the noise gets louder then just stops.

I believe my RPM is lower then your average truck since its on 3.55 gearing with 37's on it.

 

Wow! 37's with stock 3.55's!

 

3.55 gears with 37s??????

Man, thats gotta be hard on the tranny.

EDIT: Purpl, you beat me to it.