This is deeply disappointing, as it's a) totally unnecessary bureaucracy, all heat pumps are near silent; b) unfair and discriminatory, as gas boilers are far noiser but aren't subject to noise assessment; c) undermines any benefit from removing the 1 m rule.
Maximum permissible noise limits will remain and all heat pumps will still need to comply with the Microgeneration Certification Scheme Noise Planning Standard MCS 020 to be eligible for installation under permitted development.