Is seeking refuge in Allah in a voice that contains some dissatisfaction considered ill-mannered towards Allah?

Seeking refuge (isti'adha) is a form of supplication (du'a). The general principle for supplication is not to raise one's voice, as Allah Almighty says: "Invoke your Lord humbly and privately. Indeed, He does not like aggressors." There is no harm in raising one's voice unintentionally, but one must be wary of yielding to the whispers of mockery and derision.