It is now being reported on dutch news that on 11 feb in a "fleetmessage" Boeing advised customers to check RA antennae connectors because of several earlier complaints with "altimeters" (presumably Radalts).
BNR news radio is quoting Boeing:
"Boeing issued a Next-Generation 737 fleet message on Feb 11, 2009. The message asked operators to let Boeing know of any discrepancies in the radio altimeter operations. It was not a warning. Communications with our operators are considered proprietary and we can not release the message."
Link to BNR (dutch)