Have you tried cleaning the track as well as the pickup rollers on the reefers?
I have a fasttrack layout and have never had an issue with sound dropouts on these reefers.
Even though the track may appear clean, it may not be.
When I have an issue with a Loco dropping sound I go over the track with Lionels track cleaning eraser.
Then I wipe it with a paper towel dampened with 91% isopropyl alcohol. Problem solved.
A drop of Bachman EZ lube or Atlas conduct-a-lube conductive oil on the rollers pins also helps.