On a recent dive on the Hilma Hooker at a depth of about 90' I noticed that my exhale sound from my reg was noticably quieter. We dove to this depth several times prior during the trip but only this time did I notice it. As I ascended it went back to normal.The remaining dives it was normal although they were only to about 65fsw. Could it have been due to being in close proximity to the hull of the ship somehow muffling the sound. I was not within the wreck but possibly under the gunnel as the ship is on it's side. But probably within a foot or two either way. ??