Jittery Sinusoidal signal on Tek 2235--power supply issue?

[mstettle]

Hi Everyone,
     I just bought a Tek 2235 AN/USM-488 oscilloscope.   I've tested it, and is it fully functional, but there are some trace anomalies that make me think the power supply or triggering may have an issue, and I wanted your advice (I looked quickly at the Tek troubleshooting manual, but it didn't seem definitive for the symptoms).   Here are the symptoms:
- waveforms on both channels "jitter" (bounce back and forth slightly,).  This problem is intermittent, sometimes the waveforms are perfectly stable.   The jitter appears to happen less after the unit warms up.
- Sometimes very small artifacts can be seen on sinusoid waveforms (i.e. extra phosphur dots are lighting up adjacent and just below the trace, like the trace has five o'clock shadow )
- there is sometimes a very small ripple on the trace before a signal is applied.   I haven't measured it, but it is small and again, intermittent. 
Is this the "beginning" of a power supply issue?
Thank you,
Mark