problem with freezer part of Bosch Classixx KGU30605GB?

Hi, after some weeks of making funny intermittent chugging noises during which time contents suspected of part thawing/refreezing (ice crystals in sealed bags), freezer mostly now doesn't keep sufficiently low temperatures and warning light intermittently on. Contents found unfrozen one morning, emptied, turned off and on a couple of times, test cups of water found frozen next day, but warning light continues to be on/off. Help!