Suddenly my vegas pro is creating videos with a popping sound at the start of the video. The original audio is fine but it renders with a popping noise no matter what format I use. I've reinstalled drivers (built in Realtek) but to no avail. How can this be fixed?
Does this happen on all projects with different with source audio file formats?
Is it audible in preview or just with the rendered video file?
What audio format are you rendering to?
Is the noise there if you render a (audio only) PCM file?
All projects, in rendered or preview, on all codecs, and now just I confirmed.. all PCs... i.e., I installed Vegas on a fresh PC and the same thing is happening. The new PC is a different CPU and audio chipset so this should not have happened. Meanwhile on the old PC, I reinstalled Realtek drivers (I know Realtek is the bane of the PC world), updated everything, reinstalled Vegas and got the same results. I thought your idea for rending just audio was a good one and still got the same thing, see attached 
So from the large pool of pool of blame assignment, I believe this is all in Magix camp vs: Realtek, Microsoft. Just to confirm, I opened some media files that I made last year on this same machine with the issue and there was no pop. I can play other media files with no popping noise but if Vegas rendered it (recently) then there is a popping noise at the start. I thought it would be a driver issue and tried new Realtek drivers, the stock MS driver. Nothing works. So I go back to the fact that everything did work on this machine in the past, so it's probably a Magix thing.
More diagnostics: what if you put in a fadein at the beginning of (all) the audio track(s)? How about if you delete a half-second of the audio at the beginning? Does it then pop where the audio begins or still at the beginning of the video?
P.S. if it is rendered in, it's unlikely the audio driver. And if you bring the rendered file back on to the timeline, you would be able to see the noise spike in the pseudo-waveform display.