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You don't need to contact NI, the reason of clicking is when some audio starts or ends in a point different than the zero crossing (or when the instant amplitude of the sine is different than 0).

There are 2 reasons for this:
1) The sine doesn't start at phase 0, so it's starts on the middle of the waveform, with amplitude above 0 (any synth with osc retrigger or osc phase sync will work).
2) The sine doesn't end at phase 0 or zero crossing. You need to give it some release so it ends smoothly or find a synth that always ends notes at zero crossing (don't know any, but a good Reaktor or VST programmer might know how to solve this).

put a 36dB / oct low pass filter at around 100hz at the end of the chain. if that doesn't work it's your speakers/headphones or your audio driver.

I'm gonna guess and say you don't want to increase the attack of you sub because you want it punchy?
Well you will have to increase the attack because tha is how massive is with sub bass,it is not a bug most synths using pure sines do it,i'm even pretty sure when i had my virus ti that done it too.
You have a choice you can increase the attack and release to get rid of the clip and just simply draw or play your notes slightly earlier so the attack of the sub comes at the start of the bar or add a pitch envelope onto the sub oscillator with no decay or release and a very quick attack,very simple technique for getting a punchy attack in sound design and it won't clip.