I bought my L2t used from England (I live in Slovenia) and had it shipped to me. Maybe it happend on the way here because I have the exact same problem right now - sometimes is better and sometimes worse. The highs go and then they suddenly come back or I have to shut down the L2t and switch it on again which sometimes helps and sometimes not.
I just found your post here so I'll try what you did and I'll let you know if it helped...
Thanx!