Aspire 5536 On board audio

I seem to be the only person on here asking about this machine, but I'll carry on. Running W7, 64-bit.

I've just tried Skype on here for the first time and had an awful job with the microphone quality. It sounded woolly and had so many swishing whooping artefacts that it was almost unintelligible.
I poked around in the normal windows recording application turning off all effects etc and it still sounded the same. The effects still seemed to be there.
Then discovered the separate Realtek audio manager and found I could switch off noise suppression and Acoustic echo cancellation there and that each of these removed about half of the wool and whoosh sounds, leaving the actual voice sound OK. The background noise was terrible, though.

By now I had loaded in a simple recording app that provided some simple metering and compared this machine with my Aspire 2920. Talking at a reasonable level at the same relative position gave a signal to noise level of approx 33dB on the 2920 but only 12dB at best on the 5536. Fading the mic down on each machine brought the noise right down, so the noise is either the mic amp inside the machine or the positioning of the mic itself, which seems to be just above the keyboard quite close to the fan and HD etc. In contrast, the 2920 has the mic in the lid well away from moving parts.

Using a headset gets the 2920 very good, but the 5536 is still noisier, although adequate for Skype.

I just wonder if anyone else here has one of these machines and could tell me if they are all as bad as this, or whether I should dismantle and see if there is some flexible mic mounting missing.