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I suspect that, if you can still hear the motor running inside it, that your machine has suffered a clog in its tubing and passages. I advise disassembling it some, and looking into the tubing and passages.
Also, testing the suction periodically as you disassemble it, may reveal where exactly the clog or blockage has taken place.
How old is the model 760 ? and where is it usually used?
Can you still hear the motor running inside it?
Does the motor sound as loud as usual?