I've never touched a 260E but I'll assume it's the same as all the other 124's. The marble sound is usually from the plastic case breaking where the band strap holds the motor down. Somewhat common. It's pretty quick and easy to just uncover your blower motor, take it out and inspect it by hand and even jump it to check the operation. The other common problem is the voltage regulator, I can't remember off hand which color wires to ohm out but it's also fast and easy to check, should be able to do a search on here and find the specs for resistance.