The S60 was built on Volvo's P2 platform,  which was shared with other Volvo models like the S80, V70, XC70 and finally the XC90.
2001 Volvo S60 T5
... Volvo S60 2001 #9 ...
2001 Volvo S80 MPG. Avg. MPG: Mileage: 170,889 Mi.
Volvo S80 2.9
Moondust Metallic 2001 Volvo S80 T6 Exterior Photo #51494488
2001 Volvo S80 2.9 A SR Sedan
2001 Volvo V40 #6 Volvo V40 #6
If that's the case, do you feel a "thunk" when you let off the brake and hit the gas? If you do, get that car to a dealer as soon as possible ...
Volvo V70 XC AWD