AC went out so it was replaced for $2400. After a couple days it started letting off a high pitched whistle. Not consistent, but often… the AC starts losing its coolness for several minutes. After a couple minutes, it’s fine.

When driving,I accelerated and an obvious hissing noise started under engine/transmission.no power loss,no warning lights,no shifting problems. I went under truck,but could not pinpoint the source of the hissing. Any ideas?