When dryer rotates, i hear a squeal or screech. what is wrong? Also, how old is this dryer, as I am not original ower?

If your dryer is the kind with rotating drums, might be a bearing. You should disassemble it and check if can be replaced
Dryer Repair Replacing the Drum Bearing GE Part WE3M26

Dryer Repair Replacing the Rear Drum Bearing Assembly Frigidaire Part...
Dryer Repair Replacing the Rear Drum Bearing Kit Part 1 GE Part WE25M40

GE Dryer Repair Noisy or Screeching Rear Drum Bearing WE25M40

you can fine more youtube video tutoriala looking in google for terms

Youtube DRUM DRYER

There are parts inside the dryer that require periodic maintenance, such as oiling the drum wheels, replacing the drum glides - when they become worn.

Actually, it sounds like you have two problems. The belt and the bearing. The squelling is probably the belt but the screeching is probably the bearing and was the original problem that caused the belt problem.

http://www.searspartsdirect.com/partsdirect/part-number/Maytag-Parts/Dryer-Parts/40111201/0026/464/Model-SDG2606AWW/3048/0151200?keySuffixId=NA&productTypeId=0151200&searchModelNumber=SDG2606AWW&subCompDesc=Motor%20&%20fan&brandDesc=MAYTAG&modelDesc=MAYTAG-LAUNDRY&blt=11 is the belt.

http://www.searspartsdirect.com/partsdirect/part-model/Maytag-Parts/Dryer-Parts/Model-SDG2606AWW/3048/0151200/M0510056/00006 for the bearing.

You will have to take the front and top off your unit, and take out the drum to replace.

its a chore but can be taken apart.... the unit most likely either has bad rollers or the belt tensioner which is under tub is bad... has a wheel on the tensioner that guides belt adn could have a bad bearing ....good luckkkkk

glides/rollers:

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

There is a spring loaded belt tensioner, when the spring gets old and loose the belt can squeal. The belt can get old and squeal, and a bearing in any of the devices being spun by the belt can get old and squeal. Keep your hands out of the belt area when the engine is running.

Your description sounds like one or both of the rear drum supports (rollers) is bad. A quiet thumping is almost always present as the weld in the drum comes in contact with the drum supports. A binding support will squeal, and the thumping could be worse at that time. After running the dryer until the noises are present, once disassembled, you can tell if a support is bunding or rolling normally by spinning it by hand. The same goes for the idler pulley. Make sure power is disconnected from the unit befor attempting any repairs.

While the unit is disassembled for repair, make sure your your old cat is not inside.

check the belt tention. or you may need to lubricate the wheels the drum sits on.

you have answered your own question! The belt will have become loose due to age/stretching. You hear cars making the same squealing noise when thgey rev up. Its a real squeal/screech. It may possibly be the drum rubbing on the chassis due to beariing failure, but doubtful.
So on some machines the motor is on adjustable brackets that let you move the motor away from the drum pully by loosening the bolts/nuts and then re-tighten. Don't leaver the motor down and then lock off the nut/bolt as this will make the belt too tight, and cause the belt to fail or the bearing to fail over time Take the back cover off the machine and all will be revealed.
best of luck it's a simple fix if your diagnosis is correct

could be rollor wheels that support rear of drum need grease or replaceing also have a slide bearing in frount may need lub or replaced