Audio applications often suffer from the acoustic feedback problem which leads to significant sound quality degradation and howling in the worst case. Many solutions exist to minimize the effect of feedback. However, it is not trivial to evaluate these solutions. In this work, we focus on intrusive howling detection methods by comparing a test signal to a known reference signal without howling. Traditional howling detection methods are less reliable when acoustic feedback control systems make use of some decorrelation techniques, such as frequency shifting and/or probe noise injection. In this paper, we propose two new simple detection methods which are robust against these processing strategies.