I've had a problem this season with belt squeal on stock 7.4L's. I replaced all the V belts on both engines due to age earlier in the season. The replacements are NAPA belts.
On the port engine I get belt squeal some times when the engine is started and also sometimes when the throttle is open the first time.
Also get a squeal when the trim tabs are lowered usually the first time at idle. I've checked and the two belts appear tight.

any suggestions ?
Thanks,
ed

Try spray belt dressing. While the engine is off spray a small amount on the belts and pulleys....crank the engines and let them idle for a few minutes distributing the belt dressing. That should solve your problem.

Some belts can developed a polished surface on the V in the pulley and this allows the slip. The dressing adds a bit of adhesive to the surface and takes care of the problem. This is a normal issue and even happens with serpentine belts...though not as often.

Interceptor-

I chased this problem for over 6 months until I went into a NAPA store. I presented my problem with squeeling belts and the counter man went and got a blister pack of dielectric grease. He said to sparingly rub a little of the grease to the bottom (pulley side) of the belt in one area not the whole belt and then start the engine up.

I was totally amased, the squeel went away completely. He told me the dielectric grease actually softens the rubber belt. Belt drive dressing does not work at all. It actually makes matters worse. If you try this remedy, make sure you use dielectric grease and very sparingly until your issue goes away. Trust me, it will.

Magnum Thunder

I'll give that a try this afternoon.
ed

try pancake syrup, it will cause them to grab and stop squealing