Anyone good w/ cisco & willing to help w/ a switch problem I'm having?

Have a 4506 at a remote site, w/ some IP phones (some a couple years
old, some quite new) as well as pc's connected.

The newer IP phones on this switch have issues w/ calls 'cutting out',
but the older IP phones on this switch do not have this problem.

The newer IP phones on another switch (4503) in the same bldg don't
have this problem.

The 2 switches have the same SUP engines (SUP II+), the same blades (48
port, gigabit, PoE), and run the same IOS.

QOS is set the same on both switches too.

Any ideas?