Shudder when idling in drive in 2002 Altima

I have a 2002 Nissan Altima. When I am sitting at a light, there is sometimes a shudder that runs through the vehicle. If I put it in park while at a light, it doesn’t happen. Also, when I’m accelerating, there is a sound like a rattling growl coming from the front right of the vehicle. Any ideas?

What can you tell us (in detail) about the car’s maintenance over the past 3 years?
Has a mechanic looked at the motor mounts and/or transmission mounts?

New engine at 117,000 miles (Apparently you’re not supposed to let it run hot. Who woulda thunk it?) I try to keep the oil changed about every three thousand miles (except for the most recent interval -Let it go 7 months because I thought you could do that with synthetic oil. A mechanic friend told me that’s not true.) New manifold converter and oxygen sensor last year. New front brake pads last year. New tires within last month. No, the mounts have not been examined, although I thought that’s what it might have been.

While it is in the shop for motor and trans mount inspection/repair, have the mechanic change the spark plugs if they have not been changed in the past 3 years or so.

How much will a repair like that cost?