strange howle/whistle

hello,

i have a 95 mustang gt. been getting a howling whistle sound coming from my engine compartment. happens for about 5 min after start up and stops once it's warmed up. also can get it to stop if i push the clutch in and goose it a bit. stops abruptly like somthing is closing. any ideas?... vacuum, pump...?

found out it is my power steering pump