Clutch in Alternator and belt replacement

Hi. I have a 2003 Mazda 6 and heard a rattling sound in the engine ONLY when the car is in drive or reverse, never when in Park. My mechanic said it is the clutch in the alternator that is coming apart and so the Alternator - tensioner - belt all needs to be replaced for a total of almost $800. Does this seem reasonable? The parts are $383 for one item $109 for another, $37 for belt and then $225 labor. I was in a meeting when they called, so I don’t have extreme details. I am hoping any replies won’t say I am getting hosed. thanks tons.

Clutch in the alternator?

The prices sound about right. The alternator clutch is likely in reference to some models which do not use a one piece alternator pulley. It uses a clutch of sorts in the pulley. Think centrifugal clutch.
I think some Chrysler products also use an arrangement like this.

It’s overcomplication of the simple at added expense in my opinion but that’s another discussion.

The alternator pulley/overrun clutch is sometimes available separately but if this 13 year old alternator fails after handling it who pays for the replacement? Safer for the tech to replace the alternator.

Thanks to all for the replies so far. Keith, I think it is the "alternator clutch, not clutch in alternator (my error as I was in a rush chatting with my mechanic). Ok4450, not sure who you are but I trust this website/blog and thanks for the comment that the price is about right. I feel a bit better about it. I do trust this mechanic, but hate shelling out $800 for repairs. I guess it is better than a new engine or transmission. and Nevada_545, yes, I wouldn’t try to replace it myself.

An auto electric shop may know all about this. I had mine replace the alternator’s clutch pulley with a solid pulley, which they said would stop the noise. The noise changed, but did nor go away. I later took the alternator back and asked them to put on a clutch pulley. That took care of the noise. Cost was under $90. This was on a Chrysler Town and Country.

Whether the OP’s tensioner and belt should be replaced is a different albeit related manner. After 13 years it sounds reasonable to change at least the belt. I have also replaced the tensioner on a Plymouth Voyager at maybe 110,000 miles. While the belt is off, every part powered by the belt should be checked for smoothness of operation.