Q&A

 Master

Initially I would say it is a loose fan belt. Try turning on the headlights and all electrical loads heated rear windscreen, air conditioning and then accelerate, does that make the noise more noticeable. Now turn off all loads odes that make the noise go away, that would be a test to indicate a loose fan belt.
Loose of power wouldn't be associated with a looses fan belt unless the alternator isn't charging sufficiently, either way it needs to be checked out.
By the way any Service Engine Soon Light or Check Engine Light on?