Whirpool 9400 Nylon ring shreading on drum

Did you replace the belt tensioner wheel? That's what it usually is. The only other place is where the front of the drum sits on some nylon bushings or ring. Make sure nothing has come out of pockets like a screw or coin and stuck there, or nylon bushing missing. The back of the drum also has a felt that items can stick to.

Sounds like your bearings are worn and need replacing... a horrible job. The frayed plastic may mean a new drum. To replace the bearings you must remove and separate the drum which requires removing the top, front, and back panels. Lots of clips, screws, hoses, wires.... I'd take it on if this were my unit; but for a client, I'd say get a new one. This is not uncommon for these units. Sorry.

If the sound seems to come from the front of the drum it's probably the felt guides. The bottom one will wear first and make a grinding, rattle like sound. You can access it by removing the front panel which includes the door. It fits around the drum at the front. Here's a diagram. Some models have a two piece and some a one piece guide. Part 4 on this diagram is one. It's called a seal here.
If the sound comes from the rear, there is a nylon bearing and metal socket at the rear center of the drum.

http://www.partselect.com/dryer+dryer-tears-clothes+repair.htm

Most frigidaire dryers have front felt seals with nylon slides on top that the front of the drum rides on. Without M# can't be sure if yours is like this.

try changing the thread to a different type on a sample piece of fabric
if that doesn't help check the thread guide you mentioned & see if has any burrs on it, burrs can damage thread

Hi, Many dryers use rollers or wheels to support the clothes drum. When these rollers are worn, they can be noisy. You should replace the whole set of rollers at the same time. Also dryers have a tension or idler pulley that keeps tension on the main drive belt. When it's worn, it can be noisy. When that happens, don't lubricate it. Just replace it. Many dryers use nylon or plastic glides at the front of the clothes drum for support. When these are worn, they can be noisy. When that happens, replace them.

A service engineer told me he thought there was a piece of wire caught behind drum and to see if it worked its way out. It hasn't because I don't think he's right. On spin the noise is sometimes so loud it sounds like the bearings have gone. Today I removed the fluff filter and discovered what appears to be shreaded grey plastic. If I can get a copy of the machine spec I might be able to discover where this has come from. Sorry this is not a solution. But as your symptoms are so similar check your filter and see if its full of shreaded plastic.