Cracking at start of audio in exported video

I’m getting cracking for the first couple of seconds of an exported video.
The project has two files: a video file H.264 1920 x 1080, 25 fps and an audio file. .wav, 24 bit 44.1 kHz.
There’s no crackling in the original audio file.
The audio level is -9dB or lower in the region where crackling occurs.
I’ve muted the audio in the video file and am just using the audio file.
There’s no crackling when I play within Shotcut. But when I export I get cracking in the first few seconds.
I’ve turned parallel processing off when exporting.
I’ve tried reducing the volume of the audio within Shotcut.
I’ve been using ver 18.03.06 and I’ve noticed this effect on and off over the past year. It doesn’t happen for every video and when it happens it only happens for the first couple of seconds. I’m editting a new video now and found the effect yesterday with 18.03.06. I upgraded to the latest 19.10.20 and the effect is exactly the same.
I’ve done a forum search and see others with the same issue. But there doesn’t seem to be a definite fix suggested which would apply.

I saw one suggestion here that this problem could be caused by a different sample rate in the audio file to the audio in the video file.
The video file properties state codec ATSC A/52A (AC3), 48 kHz.
I converted my audi file to 24 bit, 48 kHz .wav.
This changed the behaviour. Now I get stuttering for the first few seconds when I play inside Shotcut. When I play the exported file there’s slightly different crackling at the start. But it’s still there.