knocking noise &warranty of drive train(pistons) on 2003 Subaru Forester

I took my 2003 Forester(manual trans) for an oil change with a concern about a "knocking" noise ..Dealer said it was the "pistons,but they have to take the engine apart. to be sure...
for a repair price 0f $2000 -$4000 . Isn't this part of the engine under warrant?

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4 answers
try Subaru's upper cylinder cleaner it could be as simple as carbon build up a very common problem with vehicles not serviced at Subaru
Do you have a warranty that covers the drive train?
Pistons would not give a problem in this engine unless the engine was seriously overheated in the past or had really infrequent oil changes.
The knocking noise is apparently piston slapping from the short pistons in the top end. This has been an issue from 1998 up to and including the 2004 model. I have been told by a subaru dealer that Subaru oredered a "rebuild" for this to switch the pistons back to the long pistons that came with the pre 98 model and that are now standard after 2005. I have been told that subaru will cover this cost.

Hope this helps