Donnie,
There's really no way of telling before hand. The
simplest thing to do would be to measure the noise
level with some kind of receiver, then figure there
will be some increase with a higher antenna. Basically,
whatever he has now will be the minimum of what he will
have with the tower. More than likely there won't be
much, if any, increase in noise, especially on VHF/UHF
(line if sight).
'Doc