As Roscoroo mentioned, check your engine mounts if it's more noisey in reverse - engine will be bouncing more towards the bulkhead. Try selecting first gear with handbrake on and slipping the clutch so the wheels are taking up drive, then letting the clutch in and out gently but listening out for noises from under the bonnet. Try again but in reverse. The engine will be rocking against the engine mounts. Sometimes the mounts are okay but the rubber in the mounts just need some rubber grease. You can often quiet them down by using some lube spray like WD40 - you may have to have a friend listen under the bonnet.
BTW is it manual or automatic? Front wheel drive?
If manual, select reverse (engine off!) and check if anything is loose and rubbing/scraping against the selector rod.
If automatic perhaps a valve in the auto-box is on the way out and you're hearing fluid from that? Make sure auto box is at correct level and see if there is any dirt on the auto dipstick too.
Also, the brake pads. Some have shims between the pad and the caliper and when corrosion builds up on the edge of the brake disk they can make a noise against the shims - it might be okay forward but in reverse they're catching a part of the shim that's angled more towards the disk when in reverse. I've even seen stones stuck between the caliper and brake disk that's made a similar noise too. You really need to identify which area of the vehicle the noise is coming from for us to help you.
