Even though this thread is a little older, I feel I must post here my solution as I was experiencing the same issue like the OP had. I read the solutions laid out here and I consider they are not relevant from my point of view.
My problem was, as follows: I had the same popping / cracking noise in the Aerosoft A320 cockpit as initially mentioned in this thread; the issue was the same for the other family models A321, 318, 319. I don't own yet the A330 model, but I assume the same issue might apply also to that addon. The sound popping / cracking noise appears only when I apply thrust to the engines, towards the maximum level (say, over 60-70% or more), so no issue under that threshold. The sound is applied at a constant frequency of 2-3 seconds, fixed, and as the OP said, it is audible mostly on the left channel, only with the engines running.
For reference, I am running P3D v4.5 on a i7-8700, MSI GTX 1080, 32GB 3200CL14, SSD Sata3.
Initially I thought that the A320 addon was the culprit. For comparison, I own all PMDG addons (737, 777 and 747) and no PMDG aircraft exhibits this issue. After I checked some forums, I ran across a P3d forum thread where some users explained this issue in relation to other addons, recommending to check for DPC latency issues. Not necessarily in order to isolate this issue for I kind of had given up on Aerosoft A320 addon, I accidentally stumbled upon the same issue on a default P3d v4 aircraft (I think the Constelation from JustFlight, if I recall correctly, the big 4-engine propeller old aircraft). For further illustration, since it is obvious now that the issue is not peculiar to Aerosoft A320 addon, not all P3D default aircrafts exhibit this problem: for example the fighter jets do not have this issue, so this is why, when I initially installed P3Dv4, I didn't encounter this problem.
So, I started to use LatencyMon in order to troubleshoot any possible latency issues: I disabled and enabled in sequence all devices where I could possibly do this (of course nothing vital for the system to function). Since I didn't receive any feedback from this operation, I started up a new flight in P3D with the A320 addon. During the flight I received an error message and a DirectX latency spike from LatencyMon regarding a possible driver-related latency issue, or power management / bios throttling setting for that matter. So, I enabled the Ultimate Performance power management setting, which basically restricts my CPU to min/max 100% always, along with the PCI express link state disabled (among others), and the sound issue was gone. My i7-8700 is the non-K version so I don't think I can set, after some failed BIOS setting changes, to a fixed frequency, so for me the power management setting was the best option. Although I think that also for an unlocked CPU owner, the power management setting might still be the best option, because I have come to the conclusion, given this latency issue, that this game doesn't cope well with any kind of power management setting, besides the ultimate performance one.
Why doesn't PMDG exhibit this issue? Maybe they somehow bypass the default P3D method of audio output, I don't know. My Aerosoft A32x/31x addons now run flawless without any audio issue; I still have a very small audio crackle in the default P3D Constellation addon, but changed now on a stereo sound (and maybe some other default ones, I didn't check all the others). As an aftermath, this is an obvious issue with the P3D engine and not the A320 addon, although I blame Aerosoft for not digging further into this issue. I mean, how can PMDG and A2A have flawless audio output in the cockpit and Aerosoft A320 falls victim to this shortcoming related to an old P3D engine (same PC, same settings)? All of them use the same P3D v4 environment. Restricting the CPU to 100% frequency is not a solution, it is a workaround.
I will come back if I see any other changes.