  We report results of an extensive observational campaign of the 6 cm
formaldehyde maser in the young massive stellar object IRAS18566+0408
(G37.55+0.20) conducted from 2002 to 2009. Using Arecibo, VLA, and GBT, we
discovered quasi-periodic formaldehyde flares (P ~ 237 days). Based on Arecibo
observations, we also discovered correlated variability between formaldehyde
(H2CO) and methanol (CH3OH) masers. The H2CO and CH3OH masers are not spatially
coincident, as demonstrated by different line velocities and high angular
resolution MERLIN observations. The flares could be caused by variations in the
infrared radiation field, possibly modulated by periodic accretion onto a young
binary system.
