The heater only working on settings 3 and 4 should be the heater resistor pack failed. Common issue and quick search on the site should find the answer
For the whistle noise, try take out the cabin air-filter. Remove the glovebox (2 10mm bolts) then remove the brace behind it (4 small bolts). The air filter is behind that and just pulls out. May need changing or perhaps as you say, there's something in there that shouldn't be.
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