I bought an R61 about 14 months ago and it came with a 90W AC Adapter. About 1 month ago I noticed that the adapter has started to get very hot and make a soft chirping noise. Also, the laptop seemed to get especially hot while using it. I switched to another lenovo 90W adapter that I have for my work laptop and everything seems fine with my R61. Any idea what the problem could be with the adapter?