Ford Fiesta Zetec 2004 - Low Growling Noise

[mickyz666]

Hello forum

I'm trying to identify the cause of a what is best described as a 'low growling noise' which sounds like its coming the front passenger side of the car when the car reaches 1500-2000rpm, It dosen't seem to be speed specific just when in this rev range.
The noise emits for about half a second when hitting this rev range whilst accelerating. It doesn't seem to make this noise during gear changes or decelerating without braking to fall back into this rev range or even letting the car coast down bank in neutral.

This happens across all gears during sensible, everyday driving and isn't really specific to a cold start on a morning or when at optimal running temperature.

This mainly happens when building up speed from being stationary but can also be replicated much easier by going uphill to intentionally make the engine struggle a little by purposely falling into that rev range (and refrain from changing down a gear) Its not the usual struggling noise of the engine but whatever the cause is definitely aggravated by doing so and does turn a few heads for the wrong reasons.

I took my car into the local Ford garage and a technician came out on a road test with me where I drove the car and replicated the above and he also drove the car and confirmed the noise was irregular and happily said he could put the car up on the ramps and did some checks (not sure what he actually checked for as I wasn't allowed into the workshop).
The only thing the technician could report back to me was he found a heat shield which corroded off one of its bolts was resting slightly on the steering column. - This has since been remedied but the same noise still remains.

If anyone could give me some other possible leads to aid in my investigation - I'll promptly get back to you with any findings.

Thank you in advance