I just got this SVT CL and there is this weird noise coming through one of my speakers (410), it kind of goes away as I turn the treble down, I thought it was the tweeter at first but know now that it is not! It sounds kinda like if you tap a light bulb..ya know, you can kind of hear the elements inside move (springy). Any idea what this may be? If it is a tube, what one would you check first? Thank you!