After having a complete exhaust system replaced on my 1998 Nissan Altima and still having a rumble up front under the dash board when traveling under 40 mph - my mechanic suggests having my engine mounts replaced. Does this make sense to anyone?
Rumble? From under the dash? Strange.
Get a second opinion. (tech)
Take it to a shop that will actually do a diagnosis rather than throw parts at the noise at your expense.