J.B.
healthy sleep habits, happy child- is a good book
with my kids and naptime- I try to adjust the environment to their current needs. maybe a white noise machine? or soft classical music? a white noise machine is something you could use at grandma's and your house- and would cover any extraneous noise that either place may have... could also be that grandma wears him out better??? maybe? hard to say.
white noise tends to be magic though.
good luck-