Have a SS exhaust on the old car which has a heatshield where it runs beside the gearbox. Which keeps on breaking off and rattling. It's been welded back on several times. So decided to remove it totally and use some heat wrap instead.
After removing the downpipe and then taking the shield off by cutting the couple of welds that were still holding, found that one of the original plug welds (on the top, so not visible) had pulled out leaving a hole about 5mm diameter. It could have just finally given way when I removed the shield as it didn't sound like it was blowing before.
The place I've used before for SS welding appears to be on holiday, so I found another in Forest Hill. Over the phone they quoted 90 quid. To weld up a 5mm hole. The manager said it would take 2 hours and they charge 45 quid an hour. I said ok provided I could watch it being done. This didn't appeal to him. Can't think why.