I know this is an old thread, but I came across it while I was having noise problems with a Thiel sub and thought I'd post this for the benefit of any future visitors.
I have an original Thiel SW1 (later renamed SS2 when more models were added to the subwoofer line). There have been three different amplifier modules used over time. I have the first/oldest version, with analog adjustment knobs and grab handles.
I bought my sub second-hand, and originally had a lot of digital-sounding noise coming from it, which was loud enough to be annoying and distracting. The electronics in these subs seem sensitive to interference and ground loops. The amp itself turned out to be fairly quiet once I eliminated outside problems.
The worst of my original noise turned out to be caused by my wireless router, which is in the same room. By moving the router farther away, I was able to eliminate the worst noise (which was a nasty digital sputtering or chugging sound). If you have any components with wireless network connections near your sub, these are another potential source of interference. Consider either moving them as far away as possible, or running wired ethernet connections to them and shutting off their wireless transmitters.
I also made sure to plug my router into a different circuit, just to further isolate it.
Eliminating wireless interference eliminated about 80% of the noise I was experiencing.
I was able to discover the source of most of the rest of the noise. To explain, I'll also review how these subs can be hooked up.
Thiel's subs can be set up in various configurations. I have one of Thiel's passive crossover boxes that takes the output from the power amp via speaker cables and sends a low-pass signal to the sub via an XLR cable - but does not touch the signal going to the mains. This configuration is all that's needed for stereo, and I think it's a very elegant solution.
My mains are a pair of Thiel CS3.6s. They play full range (using the untouched output from the power amp) and the passive crossover feeds the sub a low-pass signal that exactly compliments the CS3.6's natural rolloff. This is the most seamless sub integration that I've personally heard.
To use the XLR connector, your speakers need to be a Thiel model that the company makes a dedicated passive crossover for, or you need to find the very expensive (and I think now discontinued) Thiel Integrator, which is an adjustable active crossover that can be used with any speakers.
Additionally, the sub has an RCA input for home theater LFE and bass management. Since I also use the sub for SACDs and movies, I have an RCA to this input from the LFE out on my home theater preamp. This is a normal configuration - the sub can be connected with either the LFE RCA or the crossover XLR alone, or with both at the same time.
Via the RCA connector, the sub will function as a completely-normal sub in an HT system You can let the HT preamp manage bass for your mains or run the mains full-range (the preamp is not aware that the sub augments the mains in this case - all it knows is that its sending a full-range signal to the mains, and when it analyzes test tones it sees full range output - it's not aware that the sub is helping out).
In stereo you can entirely bypass the HT preamp and its bass management and let the passive crossover fill in the low end.
For me, if only the passive crossover/XLR connection is used, the amp is very quiet - still a little hiss, but with the wireless interference gone, no noise is audible at my listening position.
There is a louder hiss when the LFE RCA is connected - just barely audible at my listening position, but annoying because I'm so aware of it. This seems to be a pesky ground loop that I have not been able to eliminate. When listening to records I sometimes unplug the RCA, but this hiss is obviously a ground loop and not an inherent defect in the sub's electronics. I will keep messing with it.
Like other posters on this thread, I had wondered why no reviewers ever commented on how noisy this sub's amp was. I also wondered how it was possible for me not to have noticed this when auditioning Thiel's subs in the past.
Now I know that, while they may be overly sensitive to the environment, these subs can be made to run quietly, and probably are quite for most people.
