Mercruiser screaming tilt motor

[Hoxan]

I am trying to analyse a problem I am having with the tilt on my 2001 Bayliner 4.3 mpi - Alpha one leg. The trailer up function is working properly. When you press tilt down the leg is only going half way down with the tilt motor making a high pitiched noise. After 10 minutes of running (at low speed) it is possible to get the leg fully down. I have looked at the trouble shooting guide and think it maybe the oil has water in it - but than why does it work on the trailer function or there is air in the line or the down pressure relief valve has dirt under it - I would be surprised if this is the case as the boat has only done 140 hours. Probably the biggest hint is the screaming tilt motor.Do you have any suggestions