*****Need help Craftsman YTS 4000 Ground belt Banging when drive engauged***** PLEASE

[yts4000]

I have a 2009 YTS 4000 Model 917289283 which started banging when I let the brake pedal up
while cutting grass, soon I smelled burnt rubber (belt and pulleys were burning from friction)
I stopped tractor and dropped deck to see what was up.
Belt had slipped under the rear pulley of hydro drive in rear.
I Then noticed the idler pulley was (plastic) worn down on one side of the flat belt area (contact where belt meets pulley)]
I replaced the pulley along with new belt Everything worked fine for a week or so.
Then wam-o again the belt slipped under the pulley and smell again
This time it was a plastic vee grove pulley towards the front not the main flat one in center main.
I changed that also, now when I try to enguage the tractor it will move but not as fast but the noise is relly bad banging and jumping sort of
I went under and looked but belt and pulleys are brand new, I replaced the tension spring on main pulley assembly today but no good.
Basically every part is new and she still is banging really bad (never made this much noise and it is not normal.
Can anyone suggest where to look.
Thanks
4000

 

[yts4000]

Anyone know if Sears Craftsman tractors has a helpline?

 

[yts4000]

This song is not the normal knoking cause by the brake linkage , but is a new much louder banging sounds really bad
Thanks for any input

 

[Baby Grand]

If you haven't done it already, then remove the deck from the tractor and give it a good looking over.
Pay special attention to the spindles - sounds like you might have a bad one. With the belt removed, the blades should spin freely and smoothly. Flip it over and clean any grass debris from under the deck - I've had clumps of wet mown grass that turned to concrete when it dried out that seriously reduced blade speed and the ability to eject new clippings. Also, check the blades for "dings" ... dings happen, so no shame in that.
-Jim