OK. So here is the result of my test of the laptop power supply scope measurements of the ground pin to actual ground. There are three screen grabs with voltage and frequency measurements. The test was done as follows:
First the PS was plugged directly into the power strip and noise was noticed coming from the amplifier. Next a three pin to two pin adapter was used to lift the ground and also allow measurements at the ground pin. The scope probe was connected with the ground lead connected to the ground in one of the strip sockets and the probe tip connected to the ground output terminal on the 3 to 2 adapter. The scope was used in a single shot mode so that the trace could be loaded to a flash drive. Three measurements were taken as the noise was not constant and varied with time.
From the images, you can see there is a considerable noise with peak to peak levels reaching over 4 V and RMS values over 400 mv. There were also a wide range of frequencies with some of the highest peaks with a frequency of over 1 MHz. Nasty stuff. Once the cord is connected to the line ground some of this will be swamped out but apparently enough remains on the line considering normal line impedance to cause problems.
I connected the PS to an old Tenma 180 watt isolation transformer that has a completely isolated and faraday shielded secondary with a two prong socket and no ground connection on the secondary. The system was now dead quiet. I would feel fairly safe with this type of connection as the switchers are usually hi-pot tested for isolation with at least 2KV. Most isolation transformers also have at least the same voltage level for hi-pot testing. So I am more likely to win the lottery than to have both the PS and isolation transformer to break down at the same time. But, here comes the mandatory disclaimer. Multiple failures do happen so if you ever lift a ground connection do so at your own risk.
In addition to the screen grabs I am also including two links, one to a spec sheet on a Hammond 200 watt isolation transformer that should be more than sufficient for any reasonable laptop. The other is to Newark who will be happy to sell you one for only $91.74 on the web. The Hammond unit has a 3 wire receptacle on the secondary with the ground in use. You will have to use a ground lift plug to break the ground sneak path if you use this transformer. Remember it is being use only for safety.
http://www.hammondmfg.com/171.htmhttp://www.newark.com/hammond/171b/tran ... dp/96F5545