Strange noise coming from engine

I have a truck I'm running back to the Charlotte Oc for sni. Pulled in for the night and stuck it on high idle to keep cool but I've noticed it's making an odd noise.

(Going to try and upload a clip, but it sounds like a mini train horn.)

Noticed that the sound only happens when the fan to cool the engine isn't engaged...

Anyone got ideas?

Whoops... What I'm running might help. 2011 freightliner Columbia, I believe it's a series 60 Detroit.

I can't repair the thing, but I don't want it crapping out on me either. It's headed back to another SNI yard to be refurbished and sold I imagine.

 

I can, biggest thing is that this is a company truck...so I can't make repairs on it. For the time, I need to establish if it's something I need to call emergency maintenance on or if I can keep running. (I've got 450 miles to go before I hit the OC. So it's odd noise or emergency.)



This was just uploaded not but 5 minutes ago, so it may still be processing. The sound happens 3 times in the clip that I could count, let it keep recording after the fan cut on just in case someone could hear it still.

 

It probably does, but I couldn't tell you where it's at. (Actually, I'm very sure it does...but SNI keeps that their dirty secret.)

I lifted the hood up (posted prior to so I'd have some inkling when I got back) and let it run...

Noted two things, it only happens on high idle when the fan clutch kicks out to stop the fan. Doesn't seems to happen at all at normal idle.

Other thing was that every time the noise happened, the hose that ran from the AC compressor (...####### that had this truck before me never washed it...so some stuff is hard to tell aside from its the same as my old truck...) back to the firewall moved and shook. I'm guessing there's a leak there and the noise is air being sucked into the line. May not be the AC compressor, but I don't know of any other part that's belted above the alternator with hoses running to the front and back of the engine.

 

If it's just the AC, then I'm good...even if that were to give out I've got 60-2 air conditioning and I'm turning it in tomorrow.

Still concerned about it, I don't intend to idle tonight. If the AC is going out then I'd rather have it when it's hot and humid outside versus warm and humid.

I can post pictures of the hose that's shaking in the morning when it's light out if you'd like. But if what I said sounds right then I guess it's case closed. Run for the hills tomorrow and tell the mechanics.

 

Yeah, that's the noise. However why is it that it hasn't happened on the other trucks I've driven?

That's the primary reason I was tipped off... Though this is also the first truck I've ever had that high-idles at 1k rpm.

I didn't feed them after midnight! I swear!