Noise on the RIAA phono preAmp

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Hi,
I constructed the RIAA phono preamp from ESP site.
http://sound.westhost.com/project06.htm (the single supply one - bottom of page)

The preamp board is mounted inside the turntable and is sounding fine initially. But after about 20 to 30 mins of operation, it starts giving out strange crackling noises at irregular intervals. I dont believe the problem to be attributed to any rumbling.

Could it be because I am not using a regulated supply (about 18V) at PS output. Just the 13.2V from output to Bridge rectifier to a 1000uF Electrolytic.

Or what else could cause the problem?
 
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