Harmonic Noise

[WoodBoy]

I started having a harmonic (humming/whining) noise today when I started my truck. I will go ahead and give as much info as possible so bare with me.

The noise sounds like the humming noise an AirdogII that is mounted to the frame of the truck makes. To my knowledge I have never noticed this noise until today

I installed an MBRP Downpipe this past Thursday night, after installation I didnt notice any kind of noises that seemed out of the ordinary, which I am sure I would have noticed this noise as it is very obvious and anytime after installing something paranoid sydrome sets in lol. So the downpipe has been installed since Thursday night which was the last thing I have done to the truck besides retune from IDP to Gearhead Hot Street which I done Friday or Saturday and I have drove atleast 200 miles since I done both.

Once I crunk the truck this morning I instantly noticed the noise and it was there everytime I stopped at a redlight also. So when I got back home I checked the downpipe to find it was touching the HPFP Shield. Took off the downpipe and dented it at that point, reinstalled, found it was also touching what looks like a HPFP Feed Line clamp that is just beyond the shield, Took downpipe off and fixed that issue, now the downpipe is completely free of touching anything, but the noise still exists. From talking to Dustin, we are pretty sure it is the HPFP making the noise.

When I first drove it before fixing the downpipe today, the noise existed at all times when at idle, now the noise only seems to exists before the truck gets up to temp. I know it was there at 108* but was gone at 166*. Im going to let it cool down and verify this one more time before I try anything but was looking for any inputs if anyone else has experienced this or a fix.

 

[78f100]

Mine would do the same thing I had to back the pressure down on the AD to make it stop. What is your fuel pressure?
I also had ported rails at the time, has never done it again since putting stock rails back on.
If you can take a long pry bar or metal pipe while its running, touch it to the rail to pump lines. If it is the rail to pump line you will feel and hear the same noise in the pipe.

 

[WoodBoy]

stock LPFP, stock rails. I am forgot to mention I am going to do that tomorrow too to make sure thats for sure the point its coming from.

 

[WoodBoy]

Crunk it up later last night, ECT was 130*, no harmonic noise. Crunk it up this morning, ECT was 60*, no harmonic noise, so I tried to rev it up to maybe 1000rpm and it was slow to rev and when I let off and it went back to idle, the truck would lope like every second at idle with the FRP dropping about 200psi everytime it loped, I tried to rev it up again slightly and it was slow to rev then all of a sudden revved fine and the lope went away and idled smooth. Still no harmonic noise

 

[blk350on20s]

Sounds like your hpfp lines. Mine did it all the time and with dual pumps now it is even more noticeable. Its like a woo woo woo woo. Almost like a squeak sound. I attribute it to line harmonics. I can grab the lines and make it quiet right down.

 

[WoodBoy]

It has quit thank goodness and hasnt done it since the last time I posted knock on wood. I think when the downpipe rotated downwards and put pressure on the shield and whatever else something was touching the lines and has freed up now that it is off

 

[08BIGRIG]

If there is anything touching a hpf line, you will have that noise. I had it for a little while and I found the issue this past week. The issue was right where you are having the issue. I took out my downpipe and bent the heat shelid up a little bit more and then saw that in my build we missed the clamp on the duel fueler that is fastened to the back of the intake manifold. I put a fuel line clamp on the back of the manifold and installed the line. Reinstalled the heatsheild and downpipe, and all is good now. Cant even tell that there is a duel fueler on the truck at all. But just the smallest amount of hpf line touching something makes a lot of noise.

 

[WoodBoy]

Thanks Jerry, I believe the downpipe put pressure on either the shield or clamp because it was touching both and I got that fixed and whatever it was I guess didnt go back immediately after I fixed the downpipe touching, but went back to normal not long after.

And the post about it loping I guess is something cold weather related. It doesnt do it unless I make it do it and will only do it like if my ECT is below 60* for a reference after it has sat all night long. But like I said it will only do it if I try to make it do it again