Sounds like big ends. Like any engine they go if they're abused or
hammered. Without further description of the sounds, like what kind,
when in the rev range, etc it's difficult to tell. It could be
something as simple as the exhaust knocking on the chassis somewhere,
or it could be as major as a new bottom end or a new engine required.

If it goes for that price it's worth taking a chance, but without
seeing/hearing it I'd budget for some hefty engine repairs or
replacement if you're considering it.

Alex